A construction of a conventional hydraulic drive system, i.e., one example of a hydraulic circuit of the hydraulic drive system when applied to, e.g., a supersized hydraulic excavator in excess of 70 t-300 t, is shown in FIG. 9 along with a control system thereof.
Specifically, a hydraulic drive system shown in FIG. 9 comprises a first hydraulic pump 1a and a second hydraulic pump 1b both driven by a prime mover 4a, a third hydraulic pump 3a and a fourth hydraulic pump 3b both driven by a prime mover 4b, boom hydraulic cylinders 5a, 5b and an arm hydraulic cylinder 6 driven by a hydraulic fluid delivered from the first to fourth hydraulic pumps 1a, 1b, 3a, 3b, a bucket hydraulic cylinder 7 driven by the hydraulic fluid delivered from the first and third hydraulic pumps 1a, 3a, and a swing hydraulic motor 8 driven by the hydraulic fluid delivered from the second and fourth hydraulic pumps 1b, 3b.
The first hydraulic pump 1a is connected to the boom hydraulic cylinders 5a, 5b, the arm hydraulic cylinder 6 and the bucket hydraulic cylinder 7 through a first boom control valve 10c, a first arm control valve 10b, and a first bucket control valve 10a, respectively. The second hydraulic pump 1b is connected to the boom hydraulic cylinders 5a, 5b, the arm hydraulic cylinder 6 and the swing hydraulic cylinder 8 through a second boom control valve 10d, a second arm control valve 10e, and a first swing control valve 10f, respectively. These control valves 10a-10f constitute a first control valve group 10.
The third hydraulic pump 3a is connected to the boom hydraulic cylinders 5a, 5b, the arm hydraulic cylinder 6 and the bucket hydraulic cylinder 7 through a third boom control valve 11c, a third arm control valve 11b, and a second bucket control valve 11a, respectively. The fourth hydraulic pump 3b is connected to the boom hydraulic cylinders 5a, 5b, the arm hydraulic cylinder 6 and the swing hydraulic cylinder 8 through a fourth boom control valve 11d, a fourth arm control valve 11e, and a second swing control valve 11f, respectively. These control valves 11a-11f constitute a second control valve group 11.
The bottom sides of the boom hydraulic cylinders 5a, 5b are connected to the first and second boom control valves 10c, 10d through main lines 105 and to the third and fourth boom control valves 11c, 11d through main lines 125, while the rod sides of the boom hydraulic cylinders 5a, 5b are connected to the first and second boom control valves 10c, 10d through main lines 115 and to the third and fourth boom control valves 11c, 11d through main lines 135. The bottom side of the arm hydraulic cylinder 6 is connected to the first and second arm control valves 10b, 10e through a main line 116 and to the third and fourth arm control valves 11b, 11e through a main line 136, while the rod side of the arm hydraulic cylinder 6 is connected to the first and second arm control valves 10b, 10e through a main line 106 and to the third and fourth arm control valves 11b, 11e through a main line 126. The bottom side of the bucket hydraulic cylinder 7 is connected to the first bucket control valve 10a through a main line 107 and to the second bucket control valve 11a through a main line 127, while the rod side of the bucket hydraulic cylinder 7 is connected to the first bucket control valve 10a through a main line 117 and to the second bucket control valve 11a through a main line 137. Further, the swing hydraulic motor 8 is connected to the first swing control valve 10f through main lines 108, 118 and to the second swing control valve 11f through main lines 128, 138.
The control system for the hydraulic drive system includes a calculator 31 which receives operation signals output from control levers 32, 33 and outputs command signals to the front control valves 10a-f and 11a-f. The control levers 32, 33 are each moved in two orthogonal directions. Operating the control lever 32 in the two orthogonal directions outputs a swing operation signal and an arm operation signal, and operating the control lever 33 in the two orthogonal directions outputs a boom operation signal and a bucket operation signal.
In the above construction shown in FIG. 9, owing to later-described restrictions upon hose diameters available in the market, the main lines 105-107, 115-117, 125-127 and 135-137, i.e., high-pressure lines, are each made up of two or three hoses (or steel pipes, etc.).